The invention relates to electrostatography and more particularly to an electrophotographic printing apparatus and method for using receiver members having a variety of surfaces including smooth, textured, and rough surfaces.
An exemplary modular color printer, such as an electrographic or ink jet copier or printer, includes a number of tandemly arranged imaging-forming modules (see for example, Tombs, U.S. Pat. No. 6,184,911). Such a printer includes two or more single-color image forming stations or modules arranged in tandem and an insulating transport web for moving receiver members such as paper sheets through the image forming stations, wherein a single-color toner image is transferred from an image carrier, i.e., a photoconductor (PC) or an intermediate transfer member (ITM), to a receiver held electrostatically or mechanically to the transport web, and the single-color toner images from each of the two or more single-color image forming stations are successively laid down one upon the other to produce a plural or multicolor toner image on the receiver.
As is well known, a toner image may be formed on a PC by the sequential steps of uniformly charging the PC surface in a charging station using a corona charger, exposing the charged PC to a pattern of light in an exposure station to form a latent electrostatic image, and toning the latent electrostatic image in a development station to form a toner image on the PC surface. The toner image may then be transferred in a transfer station directly to a receiver, e.g., a paper sheet, or it may first be transferred to an ITM and subsequently transferred to the receiver. The toned receiver is then moved to a fusing station where the toner image is fused to the receiver by heat and/or pressure.
In a digital electrophotographic copier or printer, a uniformly charged PC surface may be exposed pixel by pixel using an electro-optical exposure device comprising light emitting diodes, such as for example described by Y. S. Ng et al., Imaging Science and Technology, 47th Annual Conference Proceedings (1994), pp. 622-625.
A widely practiced method of improving toner transfer is by use of so-called surface treated toners. As is well known, surface treated toner particles have adhered to their surfaces sub-micron particles, e.g., of silica, alumina, titania, and the like (so-called surface additives or surface additive particles). Surface treated toners generally have weaker adhesion to a smooth surface than untreated toners, and therefore surface treated toners can be electrostatically transferred more efficiently from a PC or an ITM to another member.
As disclosed in the Rimai et al. patent (U.S. Pat. No. 5,084,735) and in the Zaretsky and Gomes patent (U.S. Pat. No. 5,370,961), use of a compliant ITM roller coated by a thick compliant layer and a relatively thin hard overcoat improves the quality of electrostatic toner transfer from an imaging member to a receiver, as compared to a non-compliant intermediate roller.
A receiver carrying an unfused toner image may be fused in a fusing station in which a receiver carrying a toner image is passed through a nip formed by a heated compliant fuser roller in pressure contact with a hard pressure roller. Compliant fuser rollers are well known in the art. For example, the Chen et al. patent (U.S. Pat. No. 5,464,698) discloses a toner fuser member having a silicone rubber cushion layer disposed on a metallic core member, and overlying the cushion layer, a layer of a cured fluorocarbon polymer in which is dispersed a particulate filler. Also, in the Chen et al. patent application (U.S. Patent application Ser. No. 08/879,896) is disclosed an improved compliant fuser roller including three concentric layers, each of which layers includes a particulate filler.
An electrophotographic process for non-electrostatic transfer of a toned image from a photoconductive imaging member using an intermediate transfer roller with applied heat and pressure is disclosed in the Y. S. Ng et al. patent (U.S. Pat. No. 5,110,702). This process may be used for producing high-quality toner images on rough paper (paper roughness not defined in the Ng et al. patent), and full color images may be made by successive registered transfers of color separation toner images to form a composite toner color image on a receiver. The process suffers from a disadvantage in that prolonged exposure to heat by contact with the intermediate transfer roller can have a deleterious effect upon the life of the photoconductive imaging member.
According to the Dalal et al. patent (U.S. Pat. No. 5,999,201), an electrostatographic imaging method suitable for making high quality toner images on a rough recording sheet such as a rough paper employs electrostatic transfer of a sub-monolayer toner image from an imaging member to a compliant intermediate transfer member, followed by heating the toner image at a filming station, and subsequently transfusing the filmed toner image from the intermediate transfer member to a recording sheet (paper roughness not characterized quantitatively). Color images may be made by forming a composite film on the ITM from successive registered transfers of color separation toner images to the ITM, using the filming station after each transfer, with the composite film being subsequently transfused to a receiver. This method of making a full color image is more cumbersome than conventional methods employing intermediate transfer, i.e., in which a filming station is not used.
In common parlance or usage, paper roughness is an ill-defined quantity and has a subjective meaning related to the context. Thus, in ordinary speech one can speak of a xe2x80x9crough uncoated paperxe2x80x9d in comparison to a xe2x80x9crough coated paperxe2x80x9d, with the latter being generally perceived as being quite smooth. Similarly, a xe2x80x9csmooth uncoated paperxe2x80x9d might be described or perceived as quite rough. For objective comparisons of roughness or smoothness, it is necessary to have resort to various techniques which have been developed for measuring surface contour parameters, e.g., of papers.
A printing medium having predetermined physical characteristics suitable for color xerographic printing, including paper smoothness, is disclosed in the Foley et al. patent (U.S. Pat. No. 5,935,689). This patent relates to usage of a base paper having a smoothness of less than or equal to about 110 Hagerty units. In common parlance or usage, a smoothness of less than about 120 Hagerty units would generally represent a quite smooth paper. Certain papers, according to U.S. Pat. No. 5,935,689, are not intended for electrophotographical printing. These excluded classes are known in the art as xe2x80x9cKraftxe2x80x9d, xe2x80x9cTissuexe2x80x9d, xe2x80x9cMultiboardxe2x80x9d, xe2x80x9cCorrugated Mediumxe2x80x9d and xe2x80x9cRoofingxe2x80x9d papers. Smoothness of paper or other receiver can be related to a surface roughness parameter and may be measured by a variety of techniques, including the Sheffield method, the Bekk method, surface photomicrography, the Gardner gravure method, the Brush surface analyzer, and the Chapman method, all of which are briefly described in, for example, Mead Paper Knowledge (Mead Corporation, Chillicothe, Ohio, first edition, 1990, pp. 164-166). See also TAPPI Test Methods, 1994-1995, published by TAPPI Press, Atlanta, Ga. The Sheffield method in particular is widely used, and is described in TAPPI publication T 538 om-88. Commercial instruments are available, such as Model 538 Paper Smoothness Tester from Hagerty Technologies, Inc., of Queensbury, N.Y., as well as the Sheffield Paper Gage, available from Testing machines Inc., of Amityville, N.Y. The Sheffield surface roughness parameter and unit of roughness is described in, for example, G. A. Hagerty et al., TAPPI Journal, January 1998, pp. 101-106. According to U.S. Pat. No. 5,935,689, Sheffield units and Hagerty units are interchangeable terms. Sheffield units are usually referred to in the literature and are used henceforth herein.
The Kawabata et al. patent (U.S. Pat. No. 5,905,925) discloses apparatus for forming electrophotographically produced toner images on unconventional receivers, including multilayer receivers, tack film, cloth paper, and cloth, e.g., tee shirts. Process set points, e.g., for charging, transferring, fusing, are adjusted for known receiver physical characteristics, such as for example, electrical resistivity and thickness.
The Matsuda et al. patent (U.S. Pat. No. 5,925,446) teaches the use of a coated base material as a receiver, where the uncoated base material includes mechanical paper, rough paper, or recycled paper, and the receiver may further comprise a filler. The coating on the receiver is smoothed, e.g., by calendaring, prior to use of the receiver for electrophotography. According to this patent, Oken""s smoothness as measured by a method described in Japan TAPPI No. 5 must be greater than 40 sec., otherwise good transfer of a toner image to the receiver cannot be made.
A transfuse system disclosed by the Jia et al. patent (U.S. Pat. No. 6,088,565) includes transfer in a first transfer nip of a toner image to an intermediate transfer member, transfer in a second transfer nip from intermediate transfer member to a transfuse member, and combined transfer and fusing of the toner image in a third transfer nip from transfuse member to a receiver. The transfuse member is highly conformable for aiding transfer to rough substrates in the third transfer nip.
Images on textured paper are in demand by a significant segment of customers in the printing marketplace. While traditional non-electrostatographic color printing methods, e.g., offset printing, are able to produce high quality prints on textured paper, there remains a need in the electrostatographic printing industry for improved apparatus for making good quality prints, especially color prints, on a receiver having a textured or a rough surface. In particular, there is a need for improved non-thermal electrostatic transfer apparatus for transferring toner images to textured papers, because non-thermal transfer is inherently simpler for this purpose than thermally assisted transfer, e.g., as described in the above-cited U.S. Pat. Nos. 5,110,702; 5,999,201; and 6,088,565. Moreover, there remains a need to provide a printer that is capable of making good quality color prints on different types of receivers, e.g., on papers having a variety of surface roughnesses ranging from very smooth to visibly patterned.
The present invention, which provides improved electrophotographic color printing apparatus and method utilizing electrostatic transfer of toner, is for making color images on various types of receivers having different surface roughnesses or surface contouring characteristics, which various types of receivers include papers having smooth, rough, textured, patterned, or woven surfaces, as well as fabrics or fabric-reinforced sheet materials.
A modular color printer is disclosed for producing good quality images on receiver members having a variety of types of surface, which types of surface are generally characterizable by measurable surface contour parameters. Receiver members may have smooth, rough, textured, patterned, or woven surfaces, and include papers, fabrics, and fabric-reinforced sheets. The printer includes a number of tandemly arranged image-forming modules, with each module including a plurality of imaging subsystems for producing a single-color toner image. Receiver members are moved successively through the image-forming modules and from thence through a fusing station included in the printer. A single-color toner image is transferred to a receiver member in each successive module such that a full color toner image is built up on the receiver member as the receiver member moves from the first to the last module. In one aspect of the invention, at least a predetermined nominal image quality is generally achieved by a co-optimization of fusing station performance with the imaging performances of all the image-forming modules, which nominal image quality can be produced for full-color toner images made on receiver surfaces having widely differing smoothnesses. Thus, in a given module, optimized subsystems may include a pre-optimized exposure subsystem using light emitting diodes, a pre-optimized development subsystem using surface treated toners, and a pre-optimized electrostatic transfer subsystem using a compliant intermediate transfer roller. Similarly, a pre-optimized fusing subsystem preferably includes a compliant fuser roller for use in conjunction with the optimized subsystems of the modules. In another aspect of the invention, co-optimization can be augmented by adjustments of individual imaging subsystems included in each of the image-forming modules and by adjustments of the fusing subsystem, which adjustments can depend on pre-known characteristics of a particular type of receiver member surface.
Thus, in one embodiment for printing on various types of receiver members included in a predetermined set of types of receiver members, operational parameters of the pre-optimized imaging or fusing subsystems are not adjusted when receiver members included in the predetermined set of receiver members pass successively through the printer, i.e., are not operationally adjusted for the differing surface contour parameters of these receiver members. In other embodiments, pre-optimized material and operational parameters relating to the subsystems are used as base-line parameters for operation of the printer, with certain of these base-line parameters relating to individual subsystems being operationally adjustable from their base-line values so as to fine tune the resulting image quality on any particular type of suitable receiver member included in the predetermined set of types of receiver members.
Key attributes of the invention include improved ability to efficiently transfer toner images to a hill-and-valley type of surface topography on a receiver member, and also to successfully fuse toner particles, especially those toner particles in valleys, to the receiver member.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.